The invention relates to the field of data back-up systems, and in particular to a SCSI-to-IP cache storage device and method for implementing SAN over the Internet.
As we enter a new era of computing, data storage has changed its role from a secondary with respect to CPU and RAM, to a primary role in today's information world. Online data storage doubles approximately every nine months due to the increasing demand for network information services. While the importance of data storage is well-known, published literature is limited in the computer architecture research community reporting networked storage architecture. This situation will change quickly as information has surpassed raw computational power as the important commodity. This is especially true for Internet dependent businesses.
In general networked storage architectures have evolved from network-attached storage (NAS), storage area network (SAN), to more recent storage of IP (iSCSI). NAS architecture allows a storage system/device to be directly connected to a standard network, typically via the Ethernet. Clients on the network can access the NAS directly. A NAS based storage subsystem has a built-in file system to provide clients with file system functionality. SAN technology, on the other hand, provides a simple block level interface for manipulating nonvolatile magnetic media. Typically, a SAN includes networked storage devices interconnected through a dedicated Fibre Channel network. The basic premise of a SAN is to replace the current “point-to-point” infrastructure with one that allows “any-to-any” communications. A SAN provides high connectivity, scalability, and availability using a specialized network interface—the Fibre Channel network. Deploying such a specialized network usually introduces cost for implementation, maintenance, and management. iCSI is the most recent emerging technology with the goal of implementing the SAN technology over the better-understood and mature network infrastructure, the Internet (TCP/IP).
Implementing SAN over IP brings economy and convenience whereas it also raises issues such as performance and reliability. Currently, there are basically two approaches: one encapsulates SCSI protocol in TCP/IP at host bus adapter (HBA) level, and the other carries out SCSI and IP protocol conversion at a specialized switch. However, both approaches have severe performance limitations. To encapsulate SCSI protocol over IP requires a significant amount of overhead traffic for SCSI command transfers and handshaking over the Internet. Converting protocols at a switch places a special burden on an already overloaded switch and creates another specialized piece of network equipment in the SAN. Furthermore, the Internet was not designed for transferring data storage blocks. Many features such as Maximum Transfer Unit (MTU), data gram fragmentation, routing, and congestion control may become obstacles to providing enough instant bandwidth for large block transfers of storage data.
Therefore, there is a need for a system that can implements SAN over switched packet network, such as for example the Internet (TCP/IP).